1. Field of the Invention
The invention relates to a keyboard apparatus used in electronic keyboard instruments such as an electronic organ, an electronic piano, and a synthesizer, or in electric keyboard instruments.
2. Description of the Related Art
Some of conventional keyboard apparatuses used in electronic keyboard instruments such as electronic organs and electronic pianos also include mass members generally called hammers in correspondence to respective keys, so as to provide a heavy touch feeling close to a key touch feeling of an acoustic musical instrument such as a piano. The hammers pivot in linkage with a key depression operation of the respective keys to give a force depending on their movement as a reactive force against a key depression force, thereby providing a desired key depression touch feeling.
The hammers are generally formed of a metal material and extend linearly backward in a key longitudinal direction from pivotal fulcrum parts. As for an inertia moment, the relation of I=ma2 holds, where “I” is an inertia moment, “m” is a mass of the hammer and “a” is a distance from a pivotal fulcrum to a mass center (gravity center), and a touch feeling at the time of key depression can be made heavy by the inertia moment I. Therefore, even with the same mass “m”, the longer the distance “a” is, the larger mass feeling (equivalent mass) a finger receives.
Therefore, in a case where the hammers extend linearly, since the mass distribution thereof is uniform, it is not possible to secure a sufficient mass and a sufficient distance from the pivotal fulcrum to the gravity center unless the total length of each of the hammers is made long. Therefore, it is necessary to make the total length of the hammer long in order to obtain a desired touch feeling, which has posed a problem of increased depth of the keyboard apparatus.
Under such circumstances, also known is that a mass concentration part is formed by bending a rear end portion of a hammer made of a bar-shaped metal material so as to fold back the rear end portion forward, as disclosed in, for example, U.S. Pat. No. 5,834,668 B. This structure can shorten the total length of the hammer even with the same mass and shift a position of the gravity center closer to the rear end portion far from a pivotal fulcrum, thereby increasing the aforesaid equivalent mass. Consequently, it is possible to obtain a desired touch feeling without any increase in depth of a keyboard apparatus.
However, in a conventional keyboard apparatus including such hammers, an upper limit of the pivoting of the hammer is restricted in such a manner that the mass concentration part in its rear end portion touches with a mass member upper limit stopper provided near a rear end of a frame being a support member when the hammer pivots in linkage with a key at the key depression time. Since the bar-shaped metal material in the mass concentration part is folding back upward, the vicinity of a rear end of the folded part touches with the mass member upper limit stopper so that the pivoting is restricted. Therefore, it is necessary to position the mass member upper limit stopper as high as possible in order to allow the hammer to pivot at a sufficiently large angle for the purpose of obtaining a desired touch feeling.
In such a structure, the rear end portion of a frame has to be extended backward and made high, which poses a problem that not much reduction in depth of the keyboard is realized and the rear end portion becomes high. Moreover, increasing the length of the folded part of the mass concentration part for the purpose of increasing the mass of the hammer causes the position of the gravity center to shift closer to the pivotal fulcrum, which poses another problem that the aforesaid equivalent mass does not increase so much, resulting in a small effect of improving a touch feeling.